This invention relates to coating agents.
Base films such as thermoplastic resin films used for and/or as magnetic memory media, lapping materials, electrical and electronic materials, letterpress printing materials, paints, photographic materials, thermal ink transfer recording materials, thermal painting materials, etc. are required to possess surface characteristics such as smoothness, water and oil repellency, releasing property and anti-foulness. Prior art methods of providing such surface characteristics to base films include the following: (1) methods of applying a composition containing a polymerizable monomer and exposing to radiation or plasma; (2) methods of applying a coupling agent such as oligomer or silane; (3) methods of applying a composition obtained by adding a silicon-type graft copolymer to a coating agent with an organic solvent (Japanese Patent Publications Tokkai 58-154766 and 58-164656); and (4) methods of applying a composition obtained by adding a fluorine-type or silicon-type graft copolymer to an emulsion-type coating agent (Japanese Patent Publication Tokkai 60-243167). These prior art methods, however, had various drawbacks. The methods of type (1) require a special equipment and hence are uneconomical. The methods of type (2) result in inferior surface characteristics. The methods of type (3) are highly toxic and also result in inferior surface characteristics, and the methods of type (4) result in inferior surface characteristics because the composition to be applied is not homogeneous.
It is therefore an object of the present invention to eliminate such drawbacks of the prior art methods and to provide improved coating agents satisfying the requirements described above. In particular, the present invention relates to aqueous emulsion-type coating agents capable of providing improved surface characteristics to a thermoplastic resin film for thermal ink transfer recording or thermal printing materials.